electrical solution or an exorcism?

I don't really believe my house is possessed, but I've got an electrical problem that has me totally stumped. Been living in this 1979 house for two years. Out of the blue, at about 12:30am a couple of weeks ago, the courtyard lights go on by themselves. (It wakes me up and I'm a little wigged when it happened thinking, "intruder?"). Nope; they just turned themselves on. It's happened almost daily since. Most of the time (maybe a little more than half the time) it happens around (but not exactly) the same time of night. Not always, sometimes its other times of the day. All I can think is maybe one of the switches is failing.

There are two 20A 3-way switches controlling these lights; one inside and one outside in the courtyard. I'm thinking after the 30 years, the exterior switch is the likely culprit. I replace it. An hour later, the lights turn themselves on. Next day, I replaced the interior switch. Same result.

After they turn themselves on, toggling either switch on its own will not turn them off. For example, if I go the interior switch and it's in position A switching from A to B won't turn them off. A-B-A-B-A-B... they stay on. Same on the outside switch. However if I toggle a switch by one position, for example, I turn the interior switch from A to B; then go outside and do the same thing, the lights will turn off. AND, not only have I turned them off, but now both switches operate exactly as expected: either switch will turn the lights on and off.

There's no third switch that I'm aware of. No light switches in the house that I don't know what they do. I've got the original architect's electrical plan: only two switches on those lights.

You may have a short developing between the red/black travelers in your 12/3 cable. Is there any exposed cable outside? Overtightened cable clamps and staples are also possibilities. In any event you should disconnect the feed to whichever 3-way is receiving the power (probably the indoor one) until you replace the wire. If the short is occurring outside of a junction box and your house is wired with romex cable then the short is likely up against the wood framing of your house. Sparks and dried wood aren't a good combination.

I suppose that's possible, but here are a couple of things that seem odd in relation to that. I live in an all concrete house (even the roof is formed concrete slab) and the wiring is in conduit from the switch, down through the concrete block wall, under the slab and up through a concrete column to the second switch. I guess there could be a short, but nothing has disturbed this wire for 30 years. Second thing is, if there were a short would I be able to get the switches to behave the way they do? I can see where a red/black short could make the lights come on, but toggle each switch one "click" and, not only do the lights go off, but they now work exactly as you would expect. I can't make it duplicate the problem.

Once again last night after I posted this, crawled in to bed and was awakened at 12:20am with the courtyard lights coming on. It's weird that this happens so often (3/4 of the time?) within 15 minutes one way or the other of 12:30am. First thought was maybe some temperature change was creating some minute contraction of [something?] that caused the short. But given the weather has been all over the board, it seems so unlikely that would explain it.

Ah, you have conduit! First I think your 3-way is wired incorrectly. You are switching the neutral, not the hot. Additionally you have an intermittent fault between either the red or black traveler and the conduit or ground wire. Since the conduit is grounded and the 3-way is wired incorrectly it provides a path around the switch to complete the circuit. When you flip both 3-ways you move the power to the other (good) traveler clearing the fault. The fact that it always occurs around the same time -12am -is probably just because the power company's voltage is near its peak because your neighbors have all gone to bed. The increased voltage is what is allowing the damaged wire to arc over to the conduit and complete the circuit. Also if you system uses a ground wire keep it away from the back of the switches as much as possible. Accidental contact from the ground wire with the terminals on the switches would also cause this problem.

Of course this is all speculation an being that its near Halloween and all................

I've got more info that I hope will be helpful in figuring this out. I pulled the switches out again and found that the terminal that should have no current is reading ~25 volts. Would that be caused by a short?

I also found something else that I couldn't explain, but I thought someone on this forum might be able to explain why this was set up this way. Hot comes in to the inside switch. Both travelers are connected to TWO wires, a brown set that travel to the outside switch and a red/black set that I don't know where they go. The short (if there is one) must be in this red/black set as when I disconnect them, I get 0 volts on the "off" terminal instead of 25v. What purpose could this red/black serve? I've attached a diagram (the red/black set are the ones that go to the "?").

I've got more info that I hope will be helpful in figuring this out. I pulled the switches out again and found that the terminal that should have no current is reading ~25 volts. Would that be caused by a short?

I also found something else that I couldn't explain, but I thought someone on this forum might be able to explain why this was set up this way. Hot comes in to the inside switch. Both travelers are connected to TWO wires, a brown set that travel to the outside switch and a red/black set that I don't know where they go. The short (if there is one) must be in this red/black set as when I disconnect them, I get 0 volts on the "off" terminal instead of 25v. What purpose could this red/black serve? I've attached a diagram (the red/black set are the ones that go to the "?").
View attachment 14404

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Them wires go to the neighbors house and She goes to bed at 12:30am ??

No dimmers on either switch. I'm having a hard time thinking what those red/black wires could go to that would serve a purpose. I don't see how this could be relevant, but the lights these switches control are a set of seven lights scattered through out the courtyard. All wiring is in conduit under concrete slab and in concrete block walls.

For what it's worth, there not much mickey-mouse workmanship in this house. Built by a local architect for himself in 1979 and no one else has lived in the house until I bought it. The house doesn't lend itself to half assed electical projects: the ceiling/roof is concrete slab, concrete block walls, concrete slab foundation... there's virtually no way of adding anything new in the way of any type of wiring.

Hey JW - Don't throw the towel in on me yet! I'm not an electrician, but I think pretty logically, have done lots of home improvement and I'm cautious. I won't burn the house down or kill myself. I obviously was mistaken about the common terminal on switch #2 being neutral. Scratch "neutral" on that common terminal of switch #2. I'd appreciate your input on the two questions I've got so far. 1) I assume the 25v reading indicates short on the second set (red/black) wires? and, 2) Where might those red/black wires go that would make sense?

Phantom voltages can come from many sources and could be irrelevant to your situation. High impedance meters can show a voltage that a low impedance one won't, and there'd be very little current available. It's easy to see a high voltage when it is looking at a 100M-ohm load typical of a DMM. Put a reasonable load on it, and it would show zero volts.

Wouldn't 25-30 volts be a bit high for phantom voltage? And, just to reiterate, I won't get that reading if I disconnect the red/black from this circuit. Attached is a "cleaned up" (ie, the incorrect reference to neutral removed). and... I don't know if my meter is "high impedance" meter or not. It's an analog, not digital meter.

Wouldn't 25-30 volts be a bit high for phantom voltage? And, just to reiterate, I won't get that reading if I disconnect the red/black from this circuit. Attached is a "cleaned up" (ie, the incorrect reference to neutral removed). and... I don't know if my meter is "high impedance" meter or not. It's an analog, not digital meter.View attachment 14405

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maybe one of these switches is an X10 device and is being signalled from somebody else's X10 controller?

Hey JW - My multi meter is a GB Instruments GMT-12A. To conclude that the inside common was the hot, I turned off the breaker, disconnected all three wire wires from he inside switch [edit: turned the breaker back on] and checked the voltage on all three inside wires and all three terminals on the outside switch. The one indicated on my drawing (on the common terminal was only that measured any voltage, ~135v on my meter. The other two teminals on the inside switch have 7" red & black wires. Red ties into a red and brown. Black ties into a black & a brown. Outside switch has two browns.

what happens when you take the red/black wires out of the circuit? keep those disconnected and capped off and try it then, see what works or does not work. then you know what those red/black wires go to.

I don't know where the red/black wires go. I was hoping that if someone had an idea what function they'd serve, it might help me in tracking them down.

Inside switch is in a 4-switch metal box, outside switch is in a 2-switch metal box, metal conduit. all the wiring is 12 gauge.

Maybe the attached photo will help: The switch on the left is the one that controls the lights I'm having trouble with. On the inside switch, the black coming off the switch connected with a brown and black (w/blue tape, shown disconnected and next to its wire connector). The red coming off the switch connected with a brown and red (w/blue tape, shown disconnected and next to its wire connector). The loose black and red wires (they each have a piece of blue tape on them) were connected in the wire connectors they are closest to. When I pulled them out and turned the breaker back on, both 3-way switches work properly. Also, after I pulled them out, the issue with the 25v I was reading on the terminal that should have been 0v went away. The black wire with the blue tape attached to the right side of the switch is the hot one.

I just notice that other switch that is pulled out (second from the left) also has the same wiring setup: short wires from the switch connect to a brown set and black/red set. That switch is also a 3-way that controls a different outdoor light. It's on a different breaker and I'm not having any problem with that one.

(the wires I've been calling red are actually more pink, they look pink/beige in the photo).

Back to the problem circuit: if the electrician who originally installed this had wanted to put the circuit on a timer or X-10 device, would that red/black wire set have been an exceptable way of doing that (it would make the switches inoperable while that timer was on)? If so, would some short/failure at the timer or X-10 explain both the 25-30v I'm picking up and random "lights turning on" problem?

Just to circle around to where I started: for two years, these lights have worked as shown (except with the red & black connected). Out of the blue and with no other work going on, the problem cropped up.

We seem to be missing important information about the nature and function of this circuit! Without it, it is all idle speculation. We need to know what's connected to
those "extra" red & black wires. The "inside 3-way" shown is very different from the 3-way
switch next to it. It seems to be some kind of special device, probably with electronics inside it. I suggest the O.P. try to get a Mfr. and model # from the device and look online to see
if there's any info on it. I recall installing a number of special, electronic multi-way switch devices about a dozen years ago (chosen by client!), and every single one failed, with some rather bizarre symptoms, after a few years and had to be replaced with standard mechanical 3- and 4-way switches.